ScienceShot

ScienceShot: One Last Crossing Before Interstellar Space?

SAN FRANCISCO, CALIFORNIA—The two Voyager spacecraft have been speeding toward the "edge" of the solar system for 35 years, and Voyager 1 is getting close, very close, to leaving the sun's solar wind behind and entering interstellar space. But scientists announced here on Monday at the annual fall meeting of the American Geophysical Union that Voyager 1 has yet another leg of its journey to complete before escaping the solar system. The good news is that the hardy spacecraft has discovered a new region of space that planetary scientists had no idea existed. Out far beyond the orbits of Neptune and Pluto, Voyager 1 in August entered a zone where the charged particles of the solar wind escape outward to interstellar space and at least some of the cosmic rays of interstellar space leak into the bubble of solar wind called the heliosphere that the Voyagers have been traveling through. But Voyager 1 magnetic field measurements show that the spacecraft is still traveling through the magnetic field of the sun and strictly speaking still within the heliosphere. So it could be months or years before Voyager 1 makes its escape.